Retinoids are a class of compounds that comprise a four-isoprenoid unit in their molecular structures. Examples of retinoids include retinol (vitamin A), retinal, retiferol, tretinoin (all-trans-retinoic acid, e.g. retinoic acid, Retin-A), isotretinoin, alitretinoin (9-cis-retinoic acid), etretinate, acitretin, tazarotene, bexarotene and Adapalene.
Retinoids and retinoid-related compounds have important and diverse functions in a biological system, and have been used to treat various conditions such as acne, photoaging, psoriasis, ichthyosis, hair loss and tumor. However, time and/or dosage related adverse effects have been also reported. Examples of adverse effects of retinoids and retinoid-related compounds include painful tender swellings on the long bones, anorexia, skin lesions, hair loss, hepatosplenomegaly, papilloedema, bleeding, general malaise, pseudotomor cerebri and even death.
One alternative method of drug administration is topical delivery. Topical drug delivery has several advantages. This method avoids inactivation of a drug caused by first pass metabolism in the liver and gastrointestinal tract. It also provides local delivery of appropriate concentrations of a drug to the intended site of action without systemic exposure. Fishman (Fishman; Robert, U.S. Pat. No. 7,052,715) indicated that an additional problem associated with oral medications, is that the concentration levels which must be achieved in the bloodstream must be significant in order to effectively treat distal areas of pain, inflammation, or infection. These levels are often much higher than would be necessary if the drugs were accurately delivered to the particular site of pain or injury. For most of retinoids, topical administration cannot deliver an effective therapeutic level.
Therefore, a need exists in the art for novel compositions that are capable of being delivered efficiently and effectively to the action site of a condition (e.g., a disease) to prevent, reduce or treat conditions as well as minimize adverse side effects.